From DE 10 2005 048 841 B3 a filter element is known that is placed in the housing of a ventilation unit of a motor vehicle. Specifically, with this filter arrangement, guide pins of the housing correspond to guiding slots in the filter element.
By this means a mechanical coding is to be implemented that ensures that only a filter element suited for the housing is placed into this housing.
The guiding slots are oriented parallel to the fold backs or to the pleating direction of the folds of a folded bellows. In addition, the guiding slots are oriented parallel to the fold walls.
The bellows is hemmed by an edge strip into which passages have been inserted. The guide pins are run through the passages and then extend parallel to the fold walls or the fold backs.
A passage must be chosen to be somewhat larger than the maximum diameter of a guide pin, so that it can be guided with no problems through the passage.
Therefore, when passages are manufactured by stamping, for example, relatively large tools are needed, which are guided between the fold walls. These tools can damage the bellows.